Research On Palladium-catalyzed Aerobic Allylic C-H Bond Functionalization Reactions

Among the palladium-catalyzed oxidation reactions of alkenes, the Wacker-Tsujireaction undoubtedly represents a classical organic synthetic reaction, allowing thetransformation of alkenes into carbonyl compounds under the mild conditions. Methods thatswitch the selectivity of the reaction to synthesize allylic compounds have attracted moreand more attention, which provide access to introduce valuable functional groups at the C1 or C3 position selectively. In particular, in comparison with the well-known Tsuji-Trostreaction, the palladium-catalyzed direct functionalization of allylic C-H bonds does notneed for the prefunctionalization steps, having more efficient synthetic capability and morebroad application prospects. Hence, the scientists have recently performed a great deal ofresearch to improve the usefulness, the selectivity and so on. Currently, significant progressof allylic C-H bond functionalization has been achieved in alkylation, amination,oxygenation, silylation, dehydrogenation and halogenation.On the basis of the above-described background, we have performed an investigationon the methods of achieving the selectivity, and discussed the common features as well asthe mechanism. The research work of this thesis have studied the palladium-catalyzed andoxygen-involved allylic C-H bond functionalization reactions, the detailed content is asfollowing:(1) Palladium-catalyzed aerobic oxidative allylic C-H arylation of alkenes withpolyfluorobenzenes. Allylated arenes are an important class of substituted aromaticcompounds, which widely distribute in natural and bioactive molecules. We have developedan efficient,straightforward and regioselective Pd-catalyzed aerobic cross-coupling reactionof alkenes with polyfluorobenzenes, which represents one of the most atom-economicapproaches for creating of allyl-aryl bonds, affording allylic polyfluoroarenes with highselectivity. The reaction is suitable for a broad substrate scope: in addition to the aromaticalkenes, the aliphatic alkenes are also applicable to the reaction. From the viewpoint of bothatom-economy and environmental concerns, this work is an important complementary to thewell-known Tsuji-Trost reaction.(2) Palladium-catalyzed aerobic oxidative double allylic C-H oxygenation of alkenes.The reaction constitutes a strategically distinct approach for the synthesis ofα,β-unsaturated esters, in which the terminal alkenyl carbon serve as the carbon source ofthe carbonyl group, and the oxygen is used as an environmental benign oxidant.Interestingly, through inter- or intramolecular oxidative reactions, the transformation couldefficiently afford structurally diverse esters with high atom-economy. Preliminary studiesindicated that the reaction might undergo a double allylic C-H functionalization process:initially, an allylic ether is formed via the allylic C-H bond activation and oxygenation ofthe terminal alkenyl C-H bond with the alcohol; Subsequently, the allylic ether proceeds asecondary activation to react with another molecule of alcohol, affording the final productafter hydrolysis and oxidation-dehydrogenation process.